Current ElectricityCurrent Electricity

Electrons Electrons

Pn

nucleus

e-

Flow of Electrons (Path)Flow of Electrons (Path)

e-e- e-e-e-e-e- e-e-- +Electrons Flow Electrons Flow

Conventional CurrentConventional Current

e-

Conventional CurrentConventional Current

Flows Flows from from

+ + to to --

Current Current

Flow of ElectronsFlow of Electrons

Metals - Free ElectronsMetals - Free Electrons

e e e e e

CurrentCurrent

Flow of charge (q)!Flow of charge (q)!

q - Coulomb(C) q - Coulomb(C) 6.24 X 106.24 X 101818 electrons electrons

e ee e ee e e e e e eeee e

CurrentCurrent

e ee e ee e e e e e eeee e

Amount of charge passing Amount of charge passing a point in a second.a point in a second.

CurrentCurrent

Symbol - Symbol - II

Unit – Unit – Ampere (Amps)Ampere (Amps)

Amperes - Amperes - AA

Current =Current =ChargeChargeTimeTime

CurrentCurrent

CurrentCurrent = =ChargeChargeTimeTime

I =I =QQtt

CurrentCurrent

Ampere =Ampere =CoulombCoulombSecondSecond

1 A = 11 A = 1CCSS

ForceForce

e ee e ee e e e e e eeee e

VoltageVoltage

Potential DifferencePotential Difference

Electromotive Force (EMF)Electromotive Force (EMF)

Source of Electrons(Force) Source of Electrons(Force)

VoltageVoltage

Symbol - Symbol - VV

Unit – Unit – VoltVolt

Volt - Volt - VV

ResistanceResistance

Opposition to Current FlowOpposition to Current Flow

High ResistanceHigh ResistanceInsulatorInsulator

ResistanceResistance

Opposition to Current FlowOpposition to Current Flow

Low ResistanceLow ResistanceConductorConductor

ResistanceResistance

Opposition to Current FlowOpposition to Current Flow

High and Low ResistanceHigh and Low ResistanceSemiConductorSemiConductor

ResistanceResistance

Symbol - Symbol - RR

Unit – Unit – OhmOhm

Ohm - Ohm - ΩΩ

Putting it all TogetherPutting it all Together

LoadSource

Path

Schematic DiagramSchematic Diagram

I_

+V R

Source

Path

Load

Mathematical EquationMathematical Equation

I_

+V R

V = IR

Ohm’s LawOhm’s Law

Ohm’s LawThe mathematical

relationship betweenCurrent, Voltage and

Resistance.

Ohm’s Law WheelOhm’s Law Wheel

RIV

Find: V

V = IR

Ohm’s Law WheelOhm’s Law Wheel

RIV

Find: I

I = VR

Ohm’s Law WheelOhm’s Law Wheel

RIV

Find: V

R = V I

ExampleExample

I_

+V=10v R=500Ω

ExampleExample

Given: V=10v R=500Ω

RIV

Find: I = ?

I = VR

Equation: = 10V500Ω

I = 0.02A = 20mAI = 0.02A = 20mA

Homework:22-1Homework:22-1

Prob: 1,3,4,8,9, Prob: 1,3,4,8,9, 11,14,17,2011,14,17,20

Page 526, 527Page 526, 527Due: 3/20/07Due: 3/20/07

PowerPower

Power measures the rate Power measures the rate at which energy is at which energy is

transferred. In the case of transferred. In the case of electric current, charge is electric current, charge is

being transferredbeing transferred

PowerPower

Symbol - Symbol - PP

Unit – Unit – WattWatt

Watt - Watt - WW

PowerPower

Power = Current X VoltagePower = Current X Voltage

P = IVP = IV

Power WheelPower Wheel

VIP

Find: P

P = IV

Power WheelPower Wheel

VIP

Find: I

I = PV

Power WheelPower Wheel

VIP

Find: V

V = PI

Power EquationsPower Equations

VIP

P = V2

RRIV

P = IVP = I2R

Schematic SymbolsSchematic Symbols

ConductorSwitchFuseCapacitor

Resistor

Variable Resistor

Schematic SymbolsSchematic Symbols

Battery

dc generator

V Voltmeter

A Ammeter

Connection No Connection Ground

Schematic DiagramsSchematic Diagrams

Schematic DiagramsSchematic Diagrams

V

_

+R2

R1

V

A

Meter PlacementMeter Placement

Voltmeters are placed parallel to the component being

measured.

Ammeters are placed in series with the component being

measured.

Using Electric EnergyUsing Electric Energy

Energy used in an Electric Energy used in an Electric Circuit.Circuit.

P = E/tP = E/tE = PtE = Pt

Using Electric EnergyUsing Electric Energy

E = IE = I22RtRtE = IVtE = IVt

E = (VE = (V22/R)t/R)t

ExampleExample

_

+V=100v R=500Ω

How much energy is used How much energy is used in 1minute???in 1minute???

ExampleExample

Given: V=100v R=500Ω

t=1min=60s

Find: E = ?

E = V2t R

Equation:

E = (100V)2(60s) 500Ω

= 1200J1200J

Homework:22-2Homework:22-2

Practice Problems: Practice Problems: 11-1711-17

Page 517, 522Page 517, 522Due: 5/29/03Due: 5/29/03

Transmission ofTransmission ofElectric EnergyElectric Energy

Minimize Power Losses

P = I2RDecrease Current

Increase Voltage - 500,000V

The Kilowatt-HourThe Kilowatt-Hour

The Electric Company charges you for the amount of energy in

Kilowatt-Hours.

A Kilowatt-Hour is equal to 1000W delivered continuously for

1 hour(3600s).

The Kilowatt-HourThe Kilowatt-Hour

1kWh = (1000W)(1 hour) 1kWh = (1000J/s)(3600s)

1kWh = 3.6 X101kWh = 3.6 X1066 J J

E = PtE = Pt

Kilowatt-Hour ExampleKilowatt-Hour Example

A TV set draws 2.0A at 120V when operating. If the set is on 5

hours a day for 30 days, how much does it cost to run the set?

1 kilowatt-hour cost $0.12.

Kilowatt-Hour ExampleKilowatt-Hour Example

Given: V=120v I=2A

t=(5h/day)(30days)t=150h

Find: E = ? Cost

Kilowatt-Hour ExampleKilowatt-Hour Example

Equation: E = PtE = Ivt

E = (2A)(120V)(150h)E = 35000Wh = 35kWhCost = (35kWh)($0.12)Cost = $4.20Cost = $4.20

Homework:22-3Homework:22-3

Practice Problems: Practice Problems: 18-2018-20

Section ReviewSection ReviewPage: 525Page: 525

Due: 5/30/03Due: 5/30/03